PowerMockito mocked static method is calling actual class method instead of mocked class

Question

I have a function which calls a static function in java (TimeZone.getDefault()) UnitProperty.java

public String getDeviceTimeZone() {
        return TimeZone.getDefault().getID();
    }

I am trying to write unit test for this (UnitPropertyTest.java)

import...
@RunWith(PowerMockRunner.class)
@PrepareForTest(TimeZone.class)
public class UnitPropertyTest {

    @InjectMocks
    private UnitProperty unitProperty;

    @Before
    public void setup(){
        PowerMockito.mockStatic(TimeZone.class);
        unitProperty = new UnitProperty();
    }

    @Test
    public void test_getDeviceTimeZone_returns_set_time_zone() throws Exception {
        String expectedTimeZone = "mock-time-zone-value";
        when(TimeZone.getDefault().getID()).thenReturn(expectedTimeZone);
        System.out.println("Mocked Time Zone: " + TimeZone.getDefault().getID());
        assertEquals(expectedTimeZone, unitProperty.getDeviceTimeZone());
    }
}

But the test fails because:

Mocked Time Zone: mock-time-zone-value
Expected :mock-time-zone-value
Actual   :Europe/London

I am not sure why unitProperty.getDeviceTimeZone() isn't using mocked TimeZone class but instead calling the actual TimeZone's method value?

I have been searching for a while. Can anyone help me in understanding this behavior? Why isn't method in mocked class getting called?

Thanks in advance.